JPS63281512A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve a characteristic by enclosing a surface acoustic wave convolver in a metallic package and connecting a receiving case to the ground pattern of a printing wiring board in a prescribed position or providing an ground terminal in the prescribed position CONSTITUTION:A metallic package to enclose in an SAW convolver is connected to ground patterns 32 and 34 of a wiring board at plural points 37, output matching circuits 27 and 28 are arranged in the both sides of the package 26 and terminals 29 and 30 are connected. Further, the package 26 is connected to the ground pattern 32 of the wiring board 31 or to a case 33 directly in a nearest position 38 to the receiving case 33. Thus, the package 26 shields the electric coupling of the input output part of the SAW convolver, an ground current to conduct to the ground pattern around the input output terminal of the package 26 is conducted through the metallic package 33, the electric potential of the ground pattern is brought nearer to an ground electric potential and the level of an unnecessary wave due to the coupling between an input and an output can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device, and particularly to an improvement for reducing the generation of unnecessary waves in a surface acoustic wave convolver sealed in a metal package.

[Summary of the Invention] A SAW device sealed in a metal package is provided on a printed wiring board and housed in a metal case, and the metal package is placed between each input and output terminal, and the metal package is arranged between input and output terminals to connect the wiring board to the ground. It is electrically connected to the pattern at least near the signal input terminal, and further electrically connected to the ground pattern or the metal case at a position close to the metal case.

[Prior Art] Surface acoustic waves (hereinafter referred to as SAW) are attracting attention as key devices for various signal processing devices, spread frequency communication equipment, etc.
The convolver 1 basically has two input terminal pairs 2, 2' and 3°3', one output terminal 5, as shown in FIG.
Inlet juicer I0. It has two signals f(t) and g(
t) convolution output between
/f(τ)·g(t-τ)dτ is obtained at the output terminal 5.

Therefore, the output signal frequency is twice the input signal frequency,
The frequency spectra of the input signal and output signal have the relationship shown in FIG. As shown in FIG. 5, the basic unit of the SAW convolver is a mounted printed wiring board P on which the SAW convolver 6, its input matching circuits 7 and 8, and its output matching circuit 9 are mounted, and is connected to external circuits and inputs for connection. Terminal 10.1
There is one stored in case 13 with 1 added. Note 1
2 is an output terminal connected to the amplifier 14. This SA
The performance of the W convolver is mainly determined by the efficiency, which is expressed as the ratio of the output signal strength to the input signal strength, and the frequency bandwidth and the length of the area where the convolution operation is performed (equivalent to the output gate electrode length), but the signal processing Increasing the length of the gate electrode as one way to increase performance generally tends to reduce efficiency. For example, in the case of a monolithic type with ZnO/Sin, /Si layer structure, which is the most efficient SAW convolver, the output signal strength with respect to the input signal strength OdBm is approximately -40 with a gate electrode length of 20++n.
dBm, approximately -50 dBm at 40 mm.

Therefore, the output signal is usually amplified by an amplifier.

[Problems to be solved by the invention] By the way, in the SAW convolver, as in other SAW application devices such as SAW filters and SAW resonators, signals transmitted by capacitance or inductive coupling between the input and output terminals are They degrade the characteristics as unnecessary waves, but especially in the case of SAW convolvers, the ratio of output signal strength to input signal strength is relatively small compared to other SAW devices, so the relative influence is large and extreme In some cases, the output signal amplification amplifier may be saturated by unnecessary waves. FIG. 6A shows an example of the frequency characteristics of unnecessary waves between the input and output terminals of the basic unit of the SAW convolver.

For this reason, conventionally, in the case of a SAW convolver, the SAW convolver
In addition to the band delay filter or low-pass filter 16 for limiting the bandwidth of the input signal at the input section of the convolver 15, a band-pass or high-pass filter 17 is also used at the output section so that the input signal is It was necessary to prevent it from leaking into the circuit. However, adding a filter after the output terminal increases the number of components and costs of a system using a SAW convolver.

The biggest cause of unwanted waves due to coupling between input and output terminals is that the potential of the ground pattern that exists between the patterns on the printed wiring board that transmits input and output terminals or input and output signals is completely equal to the ground potential. The reason is that it has not become
This is due to the fact that the impedance of the ground pattern to high frequencies is not O. Moreover, this tendency increases as the frequency becomes higher.

Conventionally, as a method to reduce unnecessary waves, SAW cannot use a filter because the input and output signal frequencies are the same.
As a countermeasure for a circuit using an applied device, first, as shown in FIG.
There is a method of increasing the distance between the ground pattern 8' and the output terminal 19.degree. 19', or increasing the pattern area in order to lower the high frequency impedance of the ground pattern 20. However, this method is contrary to the recent trend toward miniaturization and higher density of circuits.

Further, as shown in FIG. 9, a shield plate 22 electrically connected to the ground pattern 10 between the input terminals 18, 18' and the output terminals 19, 19' is provided, and the shield plate 22 is electrically connected to the case 23 that houses the circuit. There is also a way to connect directly. However, this method has drawbacks such as limiting the reduction of the input/output terminal interval and hindering miniaturization, further weight reduction, reduction in the number of parts, and reduction in man-hours.

As shown in Figure 10, in SAW filters, etc., a widely used method is to add a differential amplifier circuit 24 to the output section to cancel out unnecessary waves input in the same phase and amplify desired waves input in the opposite phase. However, the SAW convolver basically has an unbalanced output, so this method cannot be used.

Furthermore, as a more commonly used method, as shown in Fig. 11, a ground pattern is provided around the printed circuit board, and electrical connections are made by soldering, etc. at multiple points 25 to the case 23 that houses the circuit. There is a way to quickly release the high frequency signal that flows into the ground pattern, but since the high frequency impedance in the ground pattern is not O,
If the electrical connection points between the ground pattern and the storage case 23 are set carelessly, the current flowing through the ground pattern between the input and output terminals may increase, and unnecessary waves may increase.

As described above, the conventional methods are insufficient to reduce the coupling between the input and output terminals of the SAW convolver and to suppress unnecessary waves, taking into consideration the size, weight, and cost reduction.

Therefore, an object of the present invention is to effectively suppress electrical coupling between input and output within a basic unit of a device using a SAW convolver, thereby reducing unnecessary waves.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes at least two pairs of signal input terminals, at least one pair, which are sealed in a metal package.
a surface acoustic wave convolver having two signal output terminals; and a printed wiring board mounted with a matching circuit for matching an external circuit to each of the input and output terminals of the convolver;
a grounded metal case that houses the wiring board;
Connection input for connecting the above matching circuit and external circuit.
In a surface acoustic wave device comprising an output terminal, a metal package in which the surface acoustic wave convolver is sealed is located between each of the input and output terminals, and is located between the ground pattern of the wiring board and at least near the signal input and output terminals. It is characterized in that it is electrically connected to the ground pattern of the wiring board or directly to the metal case at a position close to the metal case.

[Function] If configured as described above, the metal package in which the SAW convolver is sealed can have a shielding effect between the input and output matching circuits in the basic unit of the SAW convolver, and a more effective shielding effect on the ground pattern potential near the input and output terminals. It is possible to have an effect as a ground potential to bring the voltage close to the ground potential.

[Examples] The present invention will be described below with reference to examples shown in the drawings.
FIGS. 1(a) and 1(b) show an embodiment of the present invention as seen from the front and back sides of a wiring board.

In this embodiment, first, the metal package 26 in which the SAW convolver is sealed is electrically connected to the ground patterns 32 and 34 of the wiring board 31 at multiple points 37, and the input matching circuit 27
and output matching circuit 28 are placed on opposite sides of the package. Note that 29 is an input terminal of the input matching circuit, and 30 is an output terminal of the output matching circuit. Further, the package 26 is electrically connected to the ground pattern 32 of the wiring board 31 or directly to the case 33 at a position 38 closest to the grounded storage metal case 33. With this structure, the package 26 has the effect of shielding electrical coupling between the input and output sections of the SAW convolver unit.

In addition, by connecting the package and the wiring board ground pattern at least near the signal input/output terminals 35 and 36 of the SAW convolver package,
The ground current flowing through the ground pattern 32 around the input/output terminals of the convolver package 26 can be made to flow through the metal package 33, which has a lower high frequency impedance than the copper foil pattern on the wiring board, thus making the ground pattern potential more grounded. It becomes possible to approach the potential.

This means that the level of unnecessary waves due to coupling between input and output can be reduced. FIG. 6B shows the effect of the above embodiment of the present invention on the conventional FIG. 6A.

By the way, in the basic unit of SAW convolver,
When a ground pattern is routed around the wiring board in contact with the storage metal case, the potential on the ground pattern is highest near the input/output terminals. Therefore, quickly reducing the potential of this portion to the ground potential is an effective method for reducing unnecessary waves due to electrical coupling between the input and output of the SAW convolver unit.

As a means for implementing this, in this embodiment, the wiring board ground pattern and the metal case at ground potential are electrically connected at 37.degree. 38 near the input/output terminals of the SAW convolver unit.

FIG. 6C shows the effect of this embodiment on the conventional structure shown in FIG. 6A, which is combined with the shielding effect of the metal package described above.

FIG. 2 shows another embodiment in which a ground pin 39 is provided to directly connect the ground pattern near the input/output terminals of the SAW convolver unit to the ground of the system in which the unit is installed, without going through the storage case 33. It is.

[Effects of the Invention] As explained above, according to the present invention, the electrical coupling between the input and output of a surface acoustic wave device using two surface acoustic wave convolvers is achieved in a metal package in which the surface acoustic wave convolvers are sealed. This can be suppressed by providing the effect of a shield plate, and by making an electrical connection between the ground pattern of the printed wiring board and the storage case at a predetermined position, or by providing a ground terminal at a predetermined position, the ground pattern of the circuit board can be suppressed. By bringing the potential closer to ground potential, it is possible to reduce the level of unnecessary waves and improve characteristics.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing one embodiment of the present invention, Fig. 2 is a schematic diagram showing another embodiment of the invention, and Figs. 3, 5, 7 to 11 are respectively conventional FIG. 4 is a schematic diagram showing the SAW device, FIG. 4 is an input/output frequency spectrum diagram of the SAW convolver, and FIG. 6 is a characteristic diagram showing the difference in effects between the conventional example and the present invention. 26... SAW convolver sealed in a metal package, 27.28... Input/output matching circuit, 31... Printed wiring board, 32.34... Earth pattern. Patent a [People Clarion Co., Ltd.

Claims (3)

[Claims] (1) Matching external circuits to a surface acoustic wave convolver sealed in a metal package and having at least two pairs of signal input terminals and at least one signal output terminal, and the input/output terminal portion of the convolver. An elastic device consisting of a mounted printed wiring board on which a matching circuit is mounted, a grounded metal case that houses the wiring board inside, and connection input/output terminals for connecting the matching circuit and an external circuit. In the surface wave device, the metal package in which the surface acoustic wave convolver is sealed is located between the input and output terminal portions, and is electrically connected to the ground pattern of the wiring board at least near the signal input and output terminals. A surface acoustic wave device further characterized in that the surface acoustic wave device is electrically connected to the ground pattern of the wiring board or directly to the metal case even at a position close to the metal case. (2) The wiring board has at least an input terminal for connection with an external circuit.
A patent claim characterized in that one or more ground patterns are provided near each output terminal, and these ground patterns are electrically connected to a metal case housing the wiring board near the connection input/output terminals. The surface acoustic wave device according to item 1. (3) The wiring board has at least an input terminal for connection with an external circuit.
2. The surface acoustic wave device according to claim 1, further comprising one or more ground terminals near each output terminal.